//判断成绩，if，switch
#include <stdio.h>

int main()
{
	float s;
	int n;
	scanf("%f",&s);
	if(s>90)
	{
		n = 1;
		printf("1");
	}
	if(s>80)
	{
		n = 2;
		printf("2");
	}
	if(s>70)
	{
		n = 3;
	}
	if(s>60)
	{
		n = 4;
	}
	else 
	{
		n = 5;
	}
	switch(n)
	{
		case 1: printf("A\n"); break;
		case 2: printf("B\n"); break;
		case 3: printf("C\n"); break;
		case 4: printf("D\n"); break;
		default: printf("补考\n");break;
	}
	
	return 0;
}